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Org. Synth. 1942, 22, 50
DOI: 10.15227/orgsyn.022.0050
DIPHENYLACETYLENE
[Tolan]
Submitted by Lee Irvin Smith and M. M. Falkof.
Checked by W. E. Bachmann and Charles E. Maxwell.
1. Procedure
A solution of 45 g. (0.25 mole) of trans-stilbene in 750 ml. of ether is prepared in a 1-l. three-necked round-bottomed flask fitted with a reflux condenser, an efficient mechanical stirrer, and a dropping funnel. To the well-stirred solution there is added 13.8 ml. (43 g.; 0.27 mole) of bromine, during the course of 10 minutes. A solid begins to separate in 5 minutes, but stirring is continued for 1 hour. The product is collected on a Büchner funnel and washed with ether until it is white. The yield of stilbene dibromide, melting at 235–237°, is 65.8–69.1 g. (77–81%).
A solution of 90 g. of potassium hydroxide in 150 ml. of absolute ethanol is prepared in a 500-ml. round-bottomed flask fitted with a reflux condenser (Note 1). The solution is cooled somewhat, and the stilbene dibromide is added in several portions (Note 2). The mixture is then refluxed for 24 hours in an oil bath (Note 3). The hot mixture is poured into 750 ml. of cold water, and the product is removed by filtration and washed with 50 ml. of water. The crude diphenylacetylene is dried over calcium chloride in a vacuum desiccator for 18 hours at room temperature. The chunky, pale yellow crystals melt at 58–60° and weight 33.7–37.8 g. By recrystallization of this product from 50 ml. of 95% ethanol there is obtained 29.2–30.5 g. (66–69% based on the stilbene) of pure diphenylacetylene, which forms white needles melting at 60–61° (Note 4).
2. Notes
1. Complete solution of the alkali in the alcohol is effected by placing the flask in an oil bath at 130–140°.
2. The addition of the stilbene dibromide causes an immediate, vigorous reaction, with the evolution of heat. It is necessary to replace the reflux condenser after each addition, until boiling has ceased.
3. An electrically heated oil bath is used to maintain a constant bath temperature of 130–140°.
4. The submitters obtained the same percentage yield on runs four times this size; the time employed was the same as that described here, except for the addition of bromine, which required 30 minutes.
3. Discussion
Diphenylacetylene has been prepared by the present method;1 by the action of sodium amide on monochlorostilbene;2 by the action of potassium amide on stilbene dichloride;3 by heating 1,1-diphenyl-2-chloroethane with sodium ethoxide in a sealed tube;4 and from benzil via the hydrazone.5

References and Notes
  1. Smith and Hoehn, J. Am. Chem. Soc., 63, 1180 (1941); Söderbäck, Ann., 443, 161 (1925).
  2. Paillard and Wieland, Helv. Chim. Acta, 21, 1363 (1938).
  3. Coleman and Maxwell, J. Am. Chem. Soc., 56, 133 (1934).
  4. Buttenberg, Ann., 279, 327 (1894)
  5. Schlenk and Bergmann, Ann., 463, 76 (1928)

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

hydrazone

ethanol (64-17-5)

calcium chloride (10043-52-4)

ether (60-29-7)

bromine (7726-95-6)

Benzil (134-81-6)

potassium hydroxide (1310-58-3)

Tolan (108-88-3)

sodium ethoxide (141-52-6)

1,1-diphenyl-2-chloroethane

sodium amide (7782-92-5)

stilbene

Diphenylacetylene (501-65-5)

Stilbene dibromide (5789-30-0)

monochlorostilbene

potassium amide

stilbene dichloride

trans-Stilbene (103-30-0)